Turning 30 This Year

I'm turning 30 this year.
Never thought that I will be on this stage. I thought I will be 20s forever. But as my mom always reminded me back when I was much younger, "It's not every year that you're 18," I am not.
It's a big number for me. 30. Oh man. It seems the number welcomes me with big grin and says, "Welcome to the old-people-world."

Wait, I know, I know this is not the right attitude. But this is how I feel.
To get things more complicated, I have a fiancee who is 7 years younger. I realized that I can not really take it lightly.
Few weeks ago, as we sat together with some friends - which were all younger - and because some people were new to each other, we began to introduce ourselves. The first person mentioned her name and her age. And I went like, ouch. She was just 19, mind you. The next person was 24, and this 19 y.o. blossoming girl cheerfully joked, "Auch, you're old!" Hurray.
Then I had to face the music, I said my name and my age clearly. Bluntly. No responses this time.
About one or two weeks later, we met again, this time more secluded folks, only 5 of us. I forgot what exactly we were talking, but then someone mentioned about my pimpled face. His sister said, "Mom said you'd better go to doctor." Then one of them said, "You look fat." Not that bluntly, but that was what fell into my ears.
She continued by, "It's so lucky that you have a man who accepts you just the way you are." At this point, I stopped and looked at her. I asked her genuinely, "Do you think I am that bad?" Well of course she tried to convince me that wasn't what she trying to say.
Those comments however, lay deep down my heart. I've been more sensitive eversince.
A week from now, the same folks are planning to go for a vacation together. My dear bee seems desperately want me to join them. As much as I want to be with him, I just can't stand being with a decade younger bunch of people now. Pathetic, huh? Well, I am still able to blend with them, actually... It's just... I feel old :(